In a basic moving aperture or flying aperture shutter two apertures of different size initially are out of registry and during a film exposing operation are brought into registry. In particular, exposure at the smaller aperture is achieved by moving that aperture into the center of the larger aperture, holding the shutter in that position briefly and then moving the smaller aperture back out of position.
A problem with this type of shutter is that a portion of the larger aperture is exposed during the time that the smaller aperture is moved into and out of the position at the center of the larger aperture. The additional exposure from the portion of the larger aperture has the effect of increasing the size of the smaller aperture in the direction of movement thereof. This, in turn, increases the photographic blur circle at the film negative in the foregoing direction.